The present invention relates generally to FDM/TDM transmultiplexers employed as an interface between an FDM (frequency division multiplex) system and a TDM (time division multiplex) system, and more specifically to an FDM demultiplexer for providing wide bandwidth transmission.
Digital processing of an FDM signal for demultiplexing it into baseband signals is described in "TDM-FDM Transmultiplexer: Digital Polyphase and FFT", IEEE Transactions on Communications, Vol. COM-22, No. 9, September 1974. According to the prior art, the incoming FDM signal is digitized and converted to parallel form and filtered through digital subfilters at a sampling frequency equal to the channel bandwidth. Due to this sampling frequency, each of the resultant digital channels has a frequency response which is flat over a region narrower than the channel bandwidth.